1. Field of the Invention
The present invention relates to an adhesive application apparatus in a bookbinding apparatus and the bookbinding apparatus using this adhesive application apparatus and to an improvement in an adhesive application mechanism that applies a hot-melt adhesive to an end face of a back portion of a sheet bundle obtained by bundling as a copy.
2. Description of the Related Art
In general, this type of adhesive application apparatus is widely known as an apparatus that bundles sheets carried out from, e.g., an image forming apparatus as a copy, sets them at a predetermined adhesive applying position to be carried, provides a glue container that applies an adhesive on an end face of a back portion thereof, and performs immersion and application of an adhesive on an application roller arranged in this glue container. Further, a method for accommodating a hot melt (a hot-melt adhesive) in this glue container and controlling a temperature by using heating means is extensively adopted.
For example, Patent Document 1 (Japanese Patent Application Laid-open No. 2007-076118) suggests an apparatus that has a glue container arranged below a sheet bundle held in an upright posture and applies a predetermined amount of an adhesive by an application roller put in the glue container while moving this glue container along a back binding end face of the sheet bundle. This document discloses an apparatus in which a replenishing mechanism that supplies a solid adhesive to the glue container and heating means are provided and which uses the heating means to dissolve the solid adhesive supplied to the glue container.
When the thermally dissolvable (hot-melt) adhesive is accommodated in the glue container in this manner and it is thermally dissolved and applied to the sheet bundle, the adhesive must be replenished. In regard to this replenishment of the adhesive, when configuring the glue container with a large capacity and replenishing a large amount of adhesive at a time, there is a problem that dissolving the replenished adhesive requires a long time. This problem also occurs when, e.g., the adhesive in the glue container is solidified or semi-solidified (gelificated) to reduce an adhesive temperature during an interval that the apparatus is not utilized or the adhesive is applied.
Thus, for example, Patent Document 1 or Patent Document 2 (Japanese Patent No. 4147105) suggests an apparatus having a configuration that a glue container accommodating an adhesive is formed into a small shape with a relatively small capacity and the adhesive is supplied in accordance with a consumption state of the adhesive in the apparatus. This document discloses a replenishing mechanism having a configuration that a sensor which detects an adhesive amount is provided in the glue container and a predetermined amount of a solid adhesive is supplied in accordance with a detection signal from this sensor.
When applying the adhesive to a sheet bundle by an application roller provided in the glue container in this manner, a spin-coating mechanism that rotates a roller in the glue container and applying the adhesive with which a surface of the roller is impregnated while circulating the same cannot form and apply a uniform adhesive layer unless a fixed coating layer (the adhesive layer with which the roller is impregnated) is constantly formed on the roller surface facing an end face of the sheet bundle.
Further, for example, Patent Document 3 (Japanese Patent Application Laid-open No. 2008-001048) suggests control for increasing/decreasing a replenishing amount of an adhesive in accordance with a thickness of a sheet bundle in the above-described adhesive application mechanism as such the application roller. Likewise, Patent Document 4 (Japanese Patent Application Laid-open No. 2005-047198) and Patent Document 5 (Japanese Patent Application Laid-open No. 2005-047199) suggest increasing/decreasing a moving speed (an application speed) of a glue container and a rotating speed of the application roller (an adhesive supply amount) in accordance with a thickness of a sheet bundle.
The following problem is known in regard to the roller application mechanism that adjusts an application amount of an adhesive based on a moving speed (an applying speed) and a rotating speed (an adhesive replenishing amount) of the application roller when applying an adhesive to an end face of a sheet bundle as explained above. An application time is prolonged to affect a processing efficiency when this roller moving speed is reduced, and a sufficient amount of the adhesive cannot be supplied to the roller and an application layer cannot be uniformly held when a roller rotating speed is increased. Therefore, the moving speed and the rotating speed of the application roller are set to optimum values in accordance with properties of the adhesive, e.g., viscosity, and such set values are determined by identifying an apparatus specification and conducting experiments and others.
In this case, for example, when an optimum value is set to A4 size conforming to JIS and a bundle thickness is set to 20 mm, application unevenness of the adhesive occurs due to setting sheets to a large size (e.g., A3 size) of sheets or setting the bundle thickness to 50 mm. As to this application unevenness, the adhesive is not applied with a uniform application thickness in a longitudinal direction or a width direction (a thickness direction) of the sheets, and an insufficient portion where the adhesive layer is thin is produced. Such application unevenness results in page missing or irregularities on a spine at the time of bookbinding, thereby affecting a bookbinding quality.
The present inventor has discovered that such application unevenness of the adhesive occurs due to the following factor. This factor will now be described with reference to FIG. 12. An application roller 101 is pivotally rotatably supported in a glue container 100, and a roller lower half portion is dipped in an adhesive liquid whilst an upper half portion is exposed toward an adherend of a sheet bundle. In this state, the application roller 101 (or the glue container including the roller) is moved (an applying operation) in both front-side and back-side directions of the drawing at a moving speed Vt, and the application roller 101 is also rotated in an arrow direction in the drawing (a clockwise direction) at a speed Vr. The adhesive is applied to a sheet lower end face (a back binding surface) 102 based on this roller movement. At this time, a coating layer 105 is formed between a roller surface and the sheet lower end face 102. Further, a thickness of the coating layer 105 is an application thickness of the adhesive and, at the same time, the new adhesive in the glue container is supplied to the coating layer 105 based on rotation of the application roller 101 whilst the old adhesive is returned to the glue container.
In such an application mechanism providing an application roller, when the roller moving speed Vt is increased, the adhesive in the coating layer 105 becomes insufficient to cause the application unevenness. When this moving speed Vt of the application roller is reduced, an application time becomes long to decrease the efficiency. Furthermore, in regard to the rotating speed Vr of the application roller, a temperature of the adhesive to be applied is maintained constant by refluxing the adhesive in a liquid tank below the roller and the adhesive in the coating layer 105 above the roller. In particular, this roller speed must adequately enable circulation for scraping off the excessive adhesive once applied to the sheet end face to be returned to the liquid tank. It is, therefore, undesirable to increase the roller rotating speed Vr above an adequate value. It is to be noted that a heater element is usually included in the glue container 100 to detect a liquid temperature in the tank and control it to a predetermined temperature. This temperature is set a temperature that is higher than a melting point and maintains appropriate viscosity, and P2>P3>P1 is achieved where P1 is a temperature of the coating layer 105, P2 is a temperature of the heated portion, and P3 is a temperature of the liquid in the tank (see FIG. 1).
Thus, in regard to the application unevenness, the present inventor sets the roller rotating speed Vr that is utilized to properly maintain the temperature P1 of the coating layer 105. Therefore, a limit is produced in an adhesive amount supplied to the coating layer 105 formed on the roller upper surface. The present inventor has discovered that the application unevenness is produced from a relationship between a liquid amount in the coating layer stemmed on the roller upper surface and an application area.
It is an object of the present invention to provide an adhesive application apparatus that can form a uniform application layer even though a length or a thickness of a sheet bundle is equal to or above or below a predetermined size when applying the adhesive to an end face of the sheet bundle by an application roller.
Moreover, it is another object of the present invention to provide an adhesive application apparatus that can adjust an adhesive thickness applied by the application roller in a simple structure in accordance with an application region of a sheet bundle.